Strength comparable to that of in vivo bone and an excellent binding with in vivo bone are required of biomaterials for artificial joints and dental implants, etc. Additionally, flexibility and bendability are required of biomaterials for reconstructing skull defects and biomaterials for orthopedically treating bone-grafted sites since they need to be adapted to the shape of the skull and the bone shape in such bone-grafted sites (Non-Patent Document 1).
Osteoblast is involved in the binding between biomaterials and in vivo bone. Osteoblast is known for its high surface roughness and its high initial attachment rate at its surfaces having three-dimensional and isotropic irregularities (Non-Patent Document 2). Moreover, osteoblast is known for the occurrence of an excellent ingrowth in materials having a sequence of pores with a diameter of a few tens of micrometers or more (Non-Patent Document 3). Accordingly, the more osteoblast is being easily attached and being easily grown, the more the binding between the biomaterials and in vivo bone excels.
Ceramics such as hydroxyapatite and the like are known as examples of biomaterials used for reconstruction of bone defects. Such ceramics are porous bodies produced through a powder metallurgical process and thus, they have an advantage of excellent binding with in vivo bone. However, they are not applied to highly loaded sites since they are less flexible and have low bending strength. Alumina (aluminum oxide), which is also a ceramic but with a higher strength, is required to be made porous in order to improve the binding with in vivo bone and reduce the bending elastic modulus. The porous alumina has disadvantages to the effect that it is less flexible and that the strength thereof is insufficient.
On the other hand, titanium materials have drawn attention as biomaterials for artificial joints and dental implants due to their excellent biocompatibility, strength and corrosion resistance. However, when a titanium plate is used as the titanium materials, there is an issue to the effect that such titanium plate has poor binding with in vivo bone due to its smooth surface. In order to address this issue, punched metal, which results from punching the titanium plate, has been used. Since titanium materials have a high specific strength, they have an advantage to the effect that the strength thereof is sufficient, even when they are punched to make them porous so as to improve binding with in vivo bone and to lower elastic modulus.
Further, medical materials have been proposed which make use of titanium fibers as the titanium materials and which also make use of non-woven fabric made from such titanium fibers (Patent Document 1). Such titanium non-woven fabric is made by intertwining and stratifying the titanium fibers having a diameter of less than 100 μm and an aspect ratio of 20 or more (i.e. the ratio of the short axis to the long axis=1:20 or more) and by forming space for implanting biological hard tissue from its surface into the interior thereof. Such titanium non-woven fabric has been proposed as a biological hard tissue-inducing scaffold material which is excellent in terms of biological hard tissue inductivity and fixity. Moreover, it has been proposed that such titanium non-woven fabric can be used together with orthopedic implants such as artificial dental root implants and artificial joint implants, etc.
Incidentally, examples of a method for solidifying and molding metal powder and fibers into porous bodies include a hot pressing process and a powder metallurgical process such as a spark plasma sintering process. However, the solidification and molding through such processes are associated with calefaction and heat generation. Such calefaction and heat generation cause oxidization and embrittlement of the compacts, and also the flexibility thereof becomes poor. On the other hand, a cold pressing/shearing process is a method in which metal powder and metal fibers are solidified and molded by being loaded with a compressive load and a shearing load in an air atmosphere at room temperature (Non-Patent Document 4 and Patent Document 2).